Implantable medical devices such as pacemakers, defibrillators, neuro-stimulators, and the like are generally deployed in a housing that includes two metal halves forming a “clam-shell” assembly. Other housing materials may also be used. The housing is hermetically sealed after assembly so that body fluids surrounding the implanted device cannot penetrate the housing and disturb the electrical circuitry contained therein. It is generally very important that the housing be as small as possible and usually as flat as possible to make it easy to implant.
One or more feed-through connectors permit electrical communication to and from the electrical components and circuitry contained within the housing while at the same time maintaining the hermeticity of the device. These connections are typically used to test the device and provide electrical stimuli and/or electrical sensing within the body in which the device is implanted. However, in some cases it is desirable to be able to couple electrical signals into or out of the device without making direct electrical contact thereto. Such “non-contact” signals may be used to provide electrical energy to the device and/or send information or program instructions to or from the device either before or after it is implanted. An antenna is provided within the housing to transmit and/or receive such non-contact electrical signals. Relatively low frequency radio waves are commonly used for such purposes.
Various antenna designs have been employed in the past for such purposes. Examples are ferrite loaded coils and non-ferrite loaded coils formed on a circuit board or flexible tape. While such arrangements work, they suffer from a number of disadvantages, for example, excessive size and weight, awkward shapes which make it difficult to integrate the prior art antennas with the other components within the very cramped housing, poor electrical characteristics, and high cost of manufacture and/or assembly within the overall device. These problems are most severe with air-core antennas which, in order to have suitable electrical characteristics, are generally physically larger and, for efficient operation, are spaced apart from the walls of the housing or other significant conductive regions in the housing. The problem of providing an internal air-core antenna is exacerbated by the overriding requirement that the overall size of the implantable device be kept as small as possible and the need to accommodate within the housing, not only the antenna, but a long life battery and the electrical circuitry providing the desired sensing and/or stimulating functions.
For further discussion of implantable devices, as for example, cardiac pacemakers, reference may be made to U. S. Pat. No. 4,401,120 to HARTLAUB et al; U.S. Pat. No. 4,958,632 to DUGGAN; U.S. Pat. No. 5,052,388 to SIVULA et al, U.S. Pat. No. 5,080,096 to HOOPER et al; U.S. Pat. No. 5,088,488 to MARKOWITZ et al; U.S. Pat. No. 5,127,404 to WYBORNY et al; U.S. Pat. No. 5,154,170 to BENNETT et al; and U.S. Pat. No. 5,535,097 to RUBEN et al.
In view of the foregoing, it should be appreciated that there is an ongoing need to provide an improved implantable device having an air-core antenna and an antenna mounting structure that is physically stable, that integrates conveniently with the electrical circuitry, battery and contacts within the housing, that is easy to assemble, and that has appropriate electrical characteristics suitable for the desired application. Additional features will become apparent to one skilled in the art based on the foregoing background of the invention, the accompanying drawings, the following detailed description of a preferred embodiment and the appended claims.
As used herein, the terms “medical device,” “implantable device” and “implantable medical device” are intended to refer to a medical device for monitoring or delivering therapy or a combination thereof in a human or animal body.